As shown in FIG. 1, a wireless communication system 10 comprises elements such as client terminal or mobile station 12 and base stations 14. Other network devices which may be employed, such as a mobile switching center, are not shown. In some wireless communication systems there may be only one base station and many client terminals while in some other communication systems such as cellular wireless communication systems there are multiple base stations and a large number of client terminals communicating with each base station.
As illustrated, the communication path from the base station (BS) to the client terminal direction is referred to herein as the downlink (DL) and the communication path from the client terminal to the base station direction is referred to herein as the uplink (UL). In some wireless communication systems the client terminal or mobile station (MS) communicates with the BS in both DL and UL directions. For instance, this is the case in cellular telephone systems. In other wireless communication systems the client terminal communicates with the base stations in only one direction, usually the DL. This may occur in applications such as paging.
The base station to which the client terminal is communicating with is referred as the serving base station. In some wireless communication systems the serving base station is normally referred as the serving cell. The terms base station and a cell may be used interchangeably herein. In general, the cells that are in the vicinity of the serving cell are called neighbor cells. Similarly, in some wireless communication systems a neighbor base station is normally referred as a neighbor cell. A neighbor cell that is a candidate for handover or reselection is referred as a target cell herein. Whenever a cell becomes a serving cell for a client terminal, that cell is referred as visited cell herein.
In the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) wireless communication system, the air interface is organized into Orthogonal Frequency Division Multiplexing (OFDM) symbols, subframe and radio frames where each frame is identified by a Radio Frame Number (RFN). The RFN of a cell may be independent of the RFN of any other cell in the network. The 3GPP LTE wireless communication system air interface is specified such that when performing handovers the client terminal may not be required to know the RFN of the target cell. While the basic functionality of the LTE wireless communication system air interface can be maintained in the new serving cell after handover completion without knowing the RFN of the new serving cell, it is not possible to resume many other important functions of LTE wireless communication system air interface such as Channel State Information (CSI) measurements and reporting, Sounding Reference Signal (SRS) transmission, and the Semi-Persistent Scheduling (SPS), which require the knowledge of the RFN.
The CSI measurements and reporting from the client terminal to the base station, known as evolved NodeB (eNB) in 3GPP LTE wireless communication system, is essential for the eNB to assign resources to the client terminal in an optimum manner in the DL. Similarly, the SRS transmission from the client terminal to the eNB is essential for the eNB to assign resources to the client terminal in an optimum manner in the UL. The SPS is used for many real time services such a Voice over Internet Protocol (VoIP) and streaming services for music and video playback.
The CSI, SRS and SPS functions can only be resumed after the RFN becomes known, which is transmitted in the Physical Broadcast Channel (PBCH) of each cell. The PBCH decoding may require a minimum of 10 ms to a maximum of more than 100 ms depending on the prevailing signal conditions. In some cases, at the time of handovers the client terminal may be at the cell edge and the signal conditions may be generally poor. In such cases, the PBCH decoding at the time of handover may take longer time.